1. Field of the Invention
This invention relates to color television picture tube structures and to methods of manufacturing such structures.
2. Description of the Prior Art
Color television picture tubes comprise a viewing face panel having a three color mosaic phosphor screen or image viewing portion of the face panel, a color selection device in the form of a shadow mask having an apertured pattern aligned with the phosphor areas of the selection colors and three electron guns for projecting separate electron beams through the mask at characteristic angles to activate the respective color phosphors on the screen. Color selection is achieved by selectively controlling the intensities of the electron beams. The spacing and alignment of the mask with respect to the gun and the mosaic phosphor screen must be established with precision and maintained throughout the fabrication and life of the tube. Slight rotational or longitudinal misalignment of the mask, screen and guns will result in degradation of the images developed and their color fidelity.
Heretofore, color picture tubes have been manufacuted in sections which are sealed together following necessary internal processing and subassembly. These sections include a viewing face panel comprising a screen portion of substantially spherical curvature and an integral rim portion or skirt extendinggenerally normal from the screen portion toward a funnel section and a neck of that funnel in which the electron gun assembly is mounted. Prior to assembly of the face panel and funnel, the mosaic phosphor screen is formed on the internal surface of the screen portion and the color mask is mounted by fastening it to the rim portion. The rim portion is then sealed to the funnel and the electron gun assembly is mounted in the neck of the funnel. The tube is then sealed, evacuated and gettered.
In order to obtain the degree of precision in alignment of the mask and screen assembly, the customary practice has been to form the screen by photographic processes by exposure of photo-sensitive resists including the several phosphors through the mask. The phosphors for the three colors are applied in sequence by applying a coating to the inner face of the viewing screen, precisely mounting the mask, exposing the screen to light through a mask from a point corresponding to the position in the final assembled tube of the electron gun for the subject color, fixing the pattern of phosphors for that color and removing the unfixed phosphor containing material from the inner face of the viewing screen. The photographic process is repeated for each color component of the phosphor screen, and therefore, the mask is removed and remounted a number of times during the screen forming process. It is essential that the mask be positioned with respect to the face panel in the same position for each photographic process and in the final assembly of the tube. Therefore, the mounting arrangement for the mask must be sufficiently rigid and precise to define a unique mask position with respect to the screen. Further, the relationship of the screen and mask subsequently as mounted on the funnel to the electron guns in the neck of the funnel must also be established as a unique position axially, longitudinally and in a planar to axial or tilt relationship.
The manufacturing steps and apparatus involved in the production of color picture tubes require precision in the manufacture of the screen assembly, funnel, seal edges between the screen assembly and funnel, and the funnel neck. Variations in the surface of the glass of the viewing screen can result in unacceptable distortion. Thus rejection losses are high even in the initial glass forming of the parts. The addition of mounting elements for the mask to the rim of the screen assembly is highly critical and subject to production losses. The separable screen assembly and mask must be jigged with precision relative to the lighthouse, the light source for photographically generating the phosphor mosaic, on each sequence for developing a pattern of phosphors for a color. The seal of the screen assembly and mounted mask to the funnel is subject to the misalignments either initally or is subject to distortion during the thermal cycling of the parts, both of which must be avoided or limited to a narrow range of dimensional tolerances.
There is shown in U.S. patent application Ser. No. 594,531, filed July 9, 1975 in the names of Elgin M. Tom and Roland L. Vogelpohl and assigned to the assignee of the present application, an improved face panel-shadow mask-funnel assembly. An array of cavities on the inner surface of the face panel interfit with the studs on the mask mounting brackets to provide transverse positioning while the bracket surfaces extending outward from the studs provide abutting surfaces to the inner face of the face panel adjacent its stud receiving cavities to establish face panel-shadow mask spacing. A glass funnel receives the mask in its devergent end with precise spacing of the mask from its seal edge. Portions of the mask mounting brackets are fitted into seats in the funnel which may be cavities or depressions in the seal edge to establish the spacing, particulary the depth of entry of the mask in the funnel. When the seated bracket portions also support the face panel indexing studs and are seated in the seal edge of the funnel, a precisely related, rugged construction results be sealing those bracket portions in the face panel-funnel seal. Transverse and circumferential indexing of the mask in the funnel is enhanced by providing integral indexing or reference surfaces on the inner walls of the funnel. Radially outward biasing means on a rigid mask frame are abutted against the funnel internal reference surfaces for transverse orientation of the mask and thus the face panel. Interfitting protuberances and cavities for the biasing means and reference surfaces, as slots in bosses on the funnel inner surface engaged by studs on the biasing means, provide circumferential orientation of the mask and thus the face panel on the funnel.